Speaking Boolean

George Boole was a British mathematician who suggested that logical thought could be expressed as algebra. One of his legacies is the logical terminology recognised by most search engines. You don't have to use Boolean language when using search engines (some don't support it at all) but if you know how to use it you can gain far greater control over your searches.

The main Boolean operators are OR, AND, NOT, and NEAR. Some engines also add ADJ, FAR and BEFORE. It's easiest to understand what these terms do by looking at some examples.

OR searches for documents that match either search term.

sheep OR dip will find documents that contain references to either sheep or dip or both. This search could turn up pages referring to sheep, to sheep dipping, to food dips (such as French onion dip), to dipsticks, and so on.

AND searches for documents that match both terms.

sheep AND dip will find only those documents that refer to both sheep and dip. AND gives you much more focussed results than OR.

NOT searches for documents that do not contain the specified term.

sheep OR dip NOT guacamole will find those documents that contain a reference to sheep or to dip but which do not mention guacamole.

NEAR searches for documents that contain the specified words within the vicinity of one another. What constitutes the 'vicinity' varies from search engine to engine. It's usually from 10 to 25 words. With some engines you can specify proximity with the syntax NEAR/n, where n is the maximum number of words which can separate the two search terms.

sheep NEAR/10 dip searches for documents in which sheep appears within 10 words of dip.

ADJ searches for documents that contain the specified words right next to each other, in any order.

sheep ADJ dip will find documents containing 'sheep dip' and 'dip sheep'.

FAR searches for documents in which the search terms are 25 words or more apart from one another.

sheep FAR dip searches for documents containing both sheep and dip but separated by at least 25 words. Thus, this search will exclude any documents that contain the term "sheep dip".

BEFORE works just like AND, except that the terms must follow the specified order.

sheep BEFORE dip looks for documents containing both terms, with sheep preceding dip.

As some search engines require that you type the Boolean operators in upper case it pays to always abide by this convention.

When you use more than one operator in a search query, you can ensure the search engine analyses your query in the order you want by surrounding terms with parentheses. For example, (Laurel AND Hardy) OR (French AND Saunders).

by Rose Vines